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| United States Patent |
6,063,979
|
|
Miyata
, et al.
|
May 16, 2000
|
Method of decomposing dioxins
Abstract
A method for decomposing and eliminating dioxins contained in flyash at a
lower temperature and in a shorter time is provided, in which dioxins or
dioxins-containing materials are brought into contact with amine compounds
and/or ammonium compounds at a temperature lower than 300.degree. C.
Chlorine in dioxins reacts with amine compounds and/or ammonium compounds
and thus the dechlorination or replacement reaction of dioxin quickly
proceeds under lower temperature. The method makes it possible to
decompose dioxins under low temperature range in which dioxins have been
thought to be undecomposable.
| Inventors:
|
Miyata; Hiroshi (Tokyo, JP);
Fujiyoshi; Naoaki (Tokyo, JP);
Izumikawa; Hirofumi (Tokyo, JP);
Mashiko; Mitsuhiro (Tokyo, JP);
Fujiwara; Noboru (Tokyo, JP)
|
| Assignee:
|
Kurita Water Industries Ltd. (Tokyo, JP)
|
| Appl. No.:
|
155157 |
| Filed:
|
September 22, 1998 |
| PCT Filed:
|
January 29, 1998
|
| PCT NO:
|
PCT/JP98/00356
|
| 371 Date:
|
September 22, 1998
|
| 102(e) Date:
|
September 22, 1998
|
| PCT PUB.NO.:
|
WO98/33607 |
| PCT PUB. Date:
|
August 6, 1998 |
Foreign Application Priority Data
| Jan 30, 1997[JP] | 9-016567 |
| Nov 21, 1997[JP] | 9-321357 |
| Current U.S. Class: |
588/316; 588/251; 588/318; 588/406; 588/409 |
| Intern'l Class: |
A62D 003/00 |
| Field of Search: |
588/205,251,207,209,213
423/240 S,245.1,210,240 R
110/345
55/487,523,525
|
References Cited
U.S. Patent Documents
| 5113772 | May., 1992 | Karasek et al. | 110/345.
|
| 5260047 | Nov., 1993 | Berger | 423/245.
|
| 5358657 | Oct., 1994 | Sawyer et al.
| |
| 5925156 | Jul., 1999 | Motoki et al. | 55/487.
|
| Foreign Patent Documents |
| 0 451 133 | Oct., 1991 | EP.
| |
| 4-241880 | Aug., 1992 | JP.
| |
| 5-161822 | Jun., 1993 | JP.
| |
| 5-138149 | Jun., 1993 | JP.
| |
| 5-137813 | Jun., 1993 | JP.
| |
| 6-265133 | Sep., 1994 | JP.
| |
| 92/00794 | Jan., 1992 | WO.
| |
| 98/09716 | Mar., 1998 | WO.
| |
Primary Examiner: Griffin; Steven P.
Assistant Examiner: Nave; Eileen E.
Attorney, Agent or Firm: Kanesaka & Takeuchi
Parent Case Text
This application is a National Stage of International Application No.
PCT/JP98/00356 filed Jan. 29, 1998, now WO 98/33607.
Claims
We claim:
1. A method for decomposing dioxins or dioxins-containing materials
consisting essentially of contacting a solid material including
incineration ashes, soil and activated carbon and containing dioxins with
at least one treating chemical selected from the group consisting of amine
compounds and ammonium compounds at a temperature lower than 300.degree.
C. to decompose dioxins contained in the solid material.
2. A method for decomposing dioxins as claimed in claim 1, wherein said at
least one treating chemical has a vapor pressure which is sufficient to
promote the decomposition reaction of dioxins in the step.
3. A method for decomposing dioxins as claimed in claim 1, wherein said at
least one treating chemical is selected from the group consisting of
alkanolamines including as monoethanolamine, diethanolamine,
triethanolamine, methanolamine, and aminomethylpropanol, lower
alkyl-derived amines including diethylamine, propylamine, and
ethylenediamine, and cyclic amines including aniline.
4. A method for decomposing dioxins as claimed in claim 3, wherein said at
least one treating chemical is selected from the group consisting of
triethanolamine, diethanolamine, monoethanolamine, aniline, propylamine,
ethylendiamine, and aminomethylpropanol.
5. A method for decomposing dioxins as claimed in claim 1, wherein said at
least one treating chemical is triethanolamine and that the temperature
during the contact is at least 200.degree. C.
6. A method for decomposing dioxins as claimed in claim 1, wherein said at
least one treating chemical is diethanolamine and that the temperature
during the contact is at least 150.degree. C.
7. A method for decomposing dioxins as claimed in claim 1, wherein said at
least one treating chemical is monoethanolamine and that the temperature
during the contact is at least 20.degree. C.
8. A method for decomposing dioxins as claimed in claim 7, wherein the
temperature during the contact is at least 50.degree. C.
9. A method for decomposing dioxins as claimed in claim 1, wherein said at
least one treating chemical is selected from the group consisting of
aniline, n-propylamine, ethylenediamine, and aminomethylpropanol and that
the temperature during the contact is at least 200.degree. C.
10. A method for decomposing dioxins as claimed in claim 1, wherein said at
least one treating chemical is selected from the group consisting of
ammonia, urea, and ammonium salts.
11. A method for decomposing dioxins as claimed in claim 10, wherein said
at least one treating chemical is ammonia.
12. A method for decomposing dioxins as claimed claim 1, wherein the
temperature during the contact is at least 200.degree. C.
13. A method for decomposing dioxins as claimed in claim 1, wherein the
solid material to be treated is mixed with said at least one treating
chemical compound and then the mixture is heated.
14. A method for decomposing dioxins as claimed in claim 1, wherein said at
least one treating chemical is heated to be gasified, and that a gaseous
flow containing the resultant gas comes into contact with the materials to
be treated.
15. A method for decomposing dioxins as claimed in claim 1, wherein 0.1-10
wt % of said at least one treating chemical relative to said solid
material is contacted with said solid material for at least 3 minutes.
16. A method for decomposing dioxins as claimed in claim 15, wherein when
said solid material is contacted with the at least one treating chemical,
chlorines in dioxins react with at least one of the amine compounds and
ammonium compounds to cause dechlorination reaction leading to
detoxification of dioxins.
Description
TECHNICAL FIELD
This invention relates to a method for decomposing dioxins, and more
particularly to a method for effectively decomposing
polychloro-p-dibenzodioxins (PCDD) and polychlorodibenzofurans (these
compounds are hereinafter referred to as "dioxins") contained in flyash
and bottom ashes (these materials are hereinafter referred to as
"incineration ashes") discharged from various incineration plants such as
an incineration plant for municipal solid waste, industrial waste and/or
medical waste.
BACKGROUND OF THE INVENTION
In the incineration plants such as incineration plants for municipal solid
waste, industrial waste and/or medical waste, the dioxins precursors
including organic compounds such as phenols, benzene and acetylene, and
chlorinated aromatic compounds such as chlorophenols and chlorobenzenes
are formed during incineration. When flyash coexists in these precursors,
the precursors change to dioxins under the catalytic action of flyash, and
thus generated dioxins exist in incineration ashes.
Conventionally proposed methods for treating such dioxins-containing flyash
are as follows.
(1) To keep the dioxins-containing flyash for 1-2 hours at a temperature
between 320 and 400.degree. C. under a reductive atmosphere (for instance,
2 hours at 320.degree. C. or 1-1.5 hours at 340.degree. C.) (Hagenmaier
process, "ORGANOHALOGEN COMPOUNDS Vol. 27 (1996)" p. 147-152)
(2) A heat treatment of the dioxins-containing flyash at 300-500.degree. C.
under the existence of a dioxins formation inhibitor (JPA 4-241880). It
has been said that dioxins do not heat-decompose at a temperature lower
than 300.degree. C. This method is basically in accordance with the above
mentioned theory, decomposing dioxins at above 300.degree. C., and a
dioxins formation inhibitor is added to the flyash in order to prevent the
formation of dioxins during the heat treatment in a temperature range in
which dioxins decompose. For particulars, flyash is heated at 400.degree.
C. for 2 hours under the existence of pyridine vapor as the dioxins
formation inhibitor.
The aforementioned conventional methods have a drawback in that their high
treatment temperature and long treatment time require much energy and high
cost. Especially, in the above mentioned method (1) it is required to
perform the treatment under a reductive atmosphere such as nitrogen gas,
bringing about complexity and a high cost.
DISCLOSURE OF THE INVENTION
The object of the present invention is to solve the problems of the prior
art and to provide a method which makes it possible to decompose and
eliminate the dioxins under a low temperature region in which dioxins have
been thought not to decompose, and to perform the treatment even under the
existence of oxygen.
According to the method of the present invention for decomposing dioxins,
dioxins are decomposed by bringing dioxins or dioxins-containing materials
into contact with at least one treating chemical selected from the group
consisting of amine compounds and ammonium compounds at a temperature
lower than 300.degree. C.
According to the present invention, chlorines in dioxins react with the
amine compound and/or the ammonium compound and this reaction causes quick
dechlorination or replacement of chlorine atoms of dioxins and eventually,
the detoxifications of dioxins at a temperature below 300.degree. C., at
which dioxins have been thought usually undecomposable.
Such effect of the amine compound and/or ammonium compound to decompose
dioxins at a temperature below 300.degree. C. has been hitherto unknown.
PREFERRED EMBODIMENT OF THE INVENTION
Dioxins to be treated according to the present invention may be contained
in the exhaust gas discharged from various incineration plants such as
municipal solid waste incineration plants, industrial wastes incineration
plants, medical waste incineration plants and so on. The
dioxins-containing materials are such as incineration ash which has
dioxins adsorbed thereon, activated carbon powder used in the adsorption
treatment of dioxins, and soil contaminated with dioxins.
The amine compound as the treating chemical may be at least one of
alkanolamines such as monoethanolamine, diethanolamine, triethanolamin,
methanolamine, and aminomethylpropanol, lower alkyl-derived amines such as
diethylamine, propylamine, and ethylenediamine, and cyclic amines such as
aniline. The preferred compounds among above mentioned are
triethanolamine, diethanolamine, monoethanolamine, aniline, propylamine,
ethylendiamine, and aminomethylpropanol.
The ammonium compound as the treating chemical may be at least one of
ammonia, urea, and ammonium salts such as ammonium bicarbonate, ammonium
carbonate, ammonium hydroxide, ammonium acetate, ammonium sulfate,
ammonium phosphate, and ammonium hydrogen phosphate. The preferred
compounds among above mentioned are ammonia, urea, ammonium bicarbonate,
ammonium sulfate, and ammonium hydrogen phosphate, and the most preferred
compound is ammonia.
When at least one treating material of the amine compounds and the ammonium
compounds is brought into contact with the incineration ashes to decompose
the dioxins, it is preferred that the treating chemical is added to the
reaction system in a ratio of 0.1-10% by weight and especially 1-5% by
weight to the amount of incineration ashes. The chemical is preferable to
be added in a larger amount as the reaction temperature is lower.
The amine compounds and/or ammonium compounds to be added to the reaction
system may be in the state of either gas, liquid, or aqueous solution. As
the dioxins and the dioxins-containing materials are effectively
decomposed when they are brought into contact with at least one of the
gaseous amine compounds and the ammonium compounds, it is preferred that
the amine compounds and the ammonium compounds have a sufficiently high
vapor pressure at a temperature lower than 300.degree. C.
In case that the liquid or the aqueous solution of the treating material is
sprayed into the exhaust gas, or in case the material is preliminarily
mixed with the incineration ashes, the material is preferable to have a
vapor pressure that they are fully vaporized at a temperature lower than
300.degree. C.
As to the method in which at least one of the amine compounds and the
ammonium compounds is brought into contact with the dioxin-containing
materials to be treated, either of the following methods A, B and C can be
employed in case of the dioxin-containing materials are soil or
incineration ashes.
A: The dioxins-containing materials and the amine compounds and/or ammonium
compounds are mixed so that they are brought into contact at an ambient
temperature. Otherwise, the mixture is heated to a temperature lower than
300.degree. C. to gasify the amine compounds and/or ammonium compounds so
that the amine compounds and/or ammonium compounds in gaseous form are
brought into contact with dioxins. In these cases, it is preferable to
previously dissolve the amine compounds and/or ammonium compounds into
water or other solvents.
B: The amine compounds and/or ammonium compounds are heated to gasify at a
temperature lower than 300.degree. C., and a gas flow containing this
resultant gas is brought into contact with the dioxins-containing
materials.
C: The amine compounds and/or ammonium compounds are applied to a solid
material and then, this solid material is mixed with, or placed on the
dioxins-containing materials. After that, they are heated to a temperature
lower than 300.degree. C. In this case, preferably a gas flow is passed
through the reaction system.
In a case dioxins or dioxins-containing materials exist in gaseous form or
as floating small particles in a gas flow such as incineration exhaust
gas, the following methods D, E, and F, for example, can be employed.
D: Vapor of the amine compounds and/or ammonium compounds or a gas
containing this vapor is supplied into the above mentioned gas flow.
E: The amine compounds and/or ammonium compounds in liquid form are
supplied into the gas flow in mist or in liquid drops.
F: A solution containing amine compounds and/or ammonium compounds
dissolved in it is supplied into the gas flow in mist or in liquid drops.
In an incineration system in which a dust collector to remove flyash in the
exhaust gas is equipped, it is preferable to supply the amine compounds
and/or ammonium compounds in a gas, liquid, or solution state into the
exhaust duct before the dust collector or into the dust collector itself.
Typically, the gas temperature at the inlet of an electrostatic
precipitator is in a range from 200 to 300.degree. C., and gas temperature
at the inlet of bag filter is in a range form 140 to 230.degree. C.
Accordingly, it is preferable that the amine compounds and/or ammonium
compounds to bc supplied into the dust collector or into the duct upstream
thereof has a sufficiently high vapor pressure in a temperature range from
140 to 230.degree. C.
Usually, dioxins do not decompose at a temperature lower than 300.degree.
C. According to the present invention, the temperature at which dioxins
and the dioxins-containing materials are brought into contact with amine
compounds and/or ammonium compounds is lower than 300.degree. C.
Nevertheless, the reaction between chlorines in dioxins and the amine
compounds and/or ammonium compounds causes the dechlorination reaction or
replacement reaction leading to the detoxification of dioxins. The lowest
temperature during the contact is determined by the vapor pressure or the
ease of vaporization of the amine compounds and/or ammonium compounds.
Namely, the preferred temperatures at which the contact is made are:
ambient temperature for monoethanolamine, over 150.degree. C. for
diethanolamine, and over 200.degree. C. for triethanolamine, aniline,
n-propylamine, ethylenediamine, and aminomethylpropanol. When the amine
compounds and/or ammonium compounds are brought into contact with the
dioxins or dioxins-containing materials at a temperature over 200.degree.
C., dioxins are generally decomposed with a sufficiently high
decomposition ratio. Besides, ammonia gives a sufficiently high
decomposition ratio at over ambient temperature. Little or no improvement
in the decomposition ratio is obtained by using contact temperature higher
than 300.degree. C.
The longer the time of the contact between amine compounds and/or ammonium
compounds and materials to be treated, the higher the decomposition ratio
of dioxins, but too long a contact time makes the treatment cost too high.
According to the method of the present invention, a sufficiently high
decomposition ratio can be obtained with the contact time of typically
3-60 minutes, especially 4-40 minutes and particularly 5-30 minutes. It is
preferable that the lower the temperature during the contact, the longer
the contact time. For example, if the contact is made at ambient
temperature, a contact time of 20-40 minutes is preferable.
The contact between the amine compounds and/or ammonium compounds and the
dioxins or dioxins-containing materials can give a sufficiently high
decomposition ratio even when the contact is made in a reductive
atmosphere or in the presence of oxygen, i.e. in the open air or in the
exhaust duct. Consequently, when carrying out the method of the present
invention, the devices and the operations for the conditioning of
atmosphere are generally not necessary.
However, when the amine compounds and/or ammonium compounds are brought
into contact with dioxins or dioxins-containing materials, attention must
be paid against the explosion hazard, if the compound used has a flash
point which is lower than the temperature during the contact. If the
concentration of the compound in concern in the atmosphere in which the
contact is made is lower than the explosion limit, the explosion can
effectively be avoided. Therefore, to lower the oxygen concentration in
the atmosphere is effective for the prevention of the explosion. Examples
of such precaution include to supply to the atmosphere a gas containing
little or no oxygen, such as nitrogen, carbon dioxide, water vapor, and
combustion exhaust gas. Severer precautions must be taken if the compound
is supplied into the exhaust duct or into the dust collector. To introduce
a part of the combustion exhaust discharged from the dust collector to the
exhaust duct using a fan or the like is a preferable method because it is
a low cost method to effectively lower the oxygen concentration in the
flue gas flowing in the exhaust duct.
In treating the incineration ashes according to the method of the present
invention, an immobilization treatment of the heavy metals in the ashes
may be performed at the same time as the decomposition of the dioxins,
using a chelating agent or a heavy metal immobilization chemicals such as
phosphoric acid.
The ashes to be treated may include the activated carbon powder which has
been blown into the exhaust duct of the incineration plant in order to
remove dioxins from the incineration flue gas.
The incineration ashes and soil which have been treated according to the
method of the present invention may be, either as it is or after having
received the further treatment such as heavy metal immobilization, kept in
drums or used as land fill.
Hereinafter, the present invention will be described in more with reference
to examples and comparative examples.
EXAMPLES 1 THROUGH 4, COMPARATIVE EXAMPLE 2
A triethanolamine aqueous solution of which concentration is 5% by weight
is added to 10 grams of flyash discharged and collected from a municipal
solid waste incinerator in such a manner as to make the proportion of
triethanolamine to the flyash to be 5% by weight. The mixture was
thoroughly mixed and then heated for 10 minutes at the temperatures
specified in Table 1, respectively.
After that, the dioxins concentrations of the treatment products were
measured to give the results shown in Table 1.
COMPARATIVE EXAMPLES 1, 3 THROUGH 6
Except that water was added to the flyash instead of triethanolamine
solution and the mixture was heated to temperatures specified in Table 1,
identical treatment was carried out and dioxins concentrations of the
resultant products were measured to give the results shown in Table 1.
Moreover, the decomposition ratios in Examples 1 through 4 were calculated
according to the following equation, from the results of Examples 1
through 4 and Comparative Examples 3 through 6 in which the treatment was
made at identical temperatures with the examples but without the addition
of triethanolamine. The values of these calculations are also shown in
Table 1.
##EQU1##
TABLE 1
__________________________________________________________________________
Dioxins
Concentration
in Treatment Dioxins
Treatment Triethanolamine Products Decomposition
Example Temperature Addition (ng/g-flyash) Ratio(%)
__________________________________________________________________________
Comperative
180 none 1885 0
Example 1
Comperative 180 added 2303 --
Example 2
Comperative 200 none 2142 0
Example 3
Example 1 200 added 726 66.1
Comperative 220 none 2535 0
Example 4
Example 2 220 added 314 87.6
Comperative 250 none 2614 0
Example 5
Example 3 250 added 6.5 99.8
Comperative 290 none 2655 0
Example 6
Example 4 290 added 6.0 99.8
__________________________________________________________________________
As apparent from Table 1, by adding triethanolamine to flyash followed by
heating to temperatures from 200 to 290.degree. C., dioxins are decomposed
in high decomposition rates. Especially, when the treatment was performed
at a temperature between 250.degree. C. and 290.degree. C., more than 99%
of dioxins present in the materials are decomposed.
Meanwhile, as it is evident from Comparative Example 2, dioxins does not
decompose in spite of triethanolamine addition when the treatment is
performed at 180.degree. C. at which triethanolamine does not vaporize.
EXAMPLE 5
A glass column having a size of 20 mm.PHI..times.250 mm was filled with 3 g
of flyash discharged and collected from a municipal solid waste
incinerator. The flyash column was then topped with glass beads on which
150 mg of monoethanolamine had been applied. The column was heated to the
temperatures of ambient temperature (20.degree. C.), 50.degree. C.,
100.degree. C., 150.degree. C., 180.degree. C., 200.degree. C.,
220.degree. C., 250.degree. C. and 290.degree. C., respectively, for 20
minutes while passing air flow through the column at a rate of 15
ml/minute from the glass beads side.
Afterward, the dioxins concentrations of the treated products were measured
with the results shown in Table 2.
EXAMPLES 6, 7
Instead of monoethanolamine in the examples 1-5, diethanolamine was used in
Example 6, and triethanolamine in Example 7. For the other respects, the
experiment was carried out in the same manner as in Example 5. The
measured values of dioxins concentrations are shown in Table 2.
COMPARATIVE EXAMPLE 7
Except that nothing was applied on the glass beads, the experiment was
carried out in the same manner as in Example 5.
The dioxins residual ratio was calculated according to the following
equation from the results of Examples 5 through 7 and Comparative Example
7. The results are shown in Table 2.
##EQU2##
TABLE 2
__________________________________________________________________________
Dioxins Concentration (ng/g) (residual ratio(%) in the parentheses)
Examples and
Comperative Example
Examples 5 6 7 Comperative
Kinds of Amine Monoethanol- Diethanol- Triethanol- Example 7
Compounds amine amine amine --
__________________________________________________________________________
Treatment Temperature (.degree. C.)
Ambient 800 (60.1)
1337 (100)
1335 (100)
--
temperature
(20)
50 170 (13.0) 1337 (100) 1334 (99.9) 1335 (100)
100 120 (9.0) 1328 (99.5) -- 1340 (100)
150 97 (7.3) 245 (18.4) -- 1510 (113)
180 54 (4.0) 178 (13.3) 1912 (143) 1885 (141)
200 90 (6.7) 100 (7.5) 726 (54.4) 2142 (160)
220 48 (3.6) 93 (7.0) 314 (23.5) 2530 (190)
250 39 (2.9) 50 (3.7) 6.5 (0.5) 2614 (196)
290 -- -- 6.0 (0.4) 2665 (200)
__________________________________________________________________________
As apparent from Table 2, in Comparative Example 7 in which no amine
compound was used, heating of flyash increases the dioxins concentration
showing that in this temperature range, only the generation of dioxins
occurs and decomposition reaction does not. On the other hand, in the
Examples 5 through 7 where different amine compounds were brought into
contact with flyash, dioxins are effectively decomposed. It is also shown
that the lower limit of temperature for decomposition is different by
amine compounds. Namely, monoethanolamine shows a decomposition ratio of
over 90% at 100.degree. C., and 80% even at 50.degree. C., while
diethanolamine and triethanolamine give high decomposition ratios at over
150.degree. C. and over 200.degree. C., respectively.
EXAMPLES 8, 9, 10, 11
Experiments were carried out in the same manner as Example 5 except that
aniline, n-propylamine, ethylenediamine, and aninomethylpropanol were used
as amine compounds in Examples 8, 9, 10, and 11, respectively, and that
the treatment temperatures were set at 250.degree. C. Residual
concentrations and decomposition ratios of dioxins are shown in Table 3.
EXAMPLE 12
An experiment was carried out in the same manner as Example 5 except that
aqueous solution of ammonia was used instead of monoethanolamine and
treatment temperature was set at 250.degree. C. Residual concentrations
and decomposition ratios of dioxins are shown in Table 3. The application
quantity of ammonia (NH.sub.3) on glass beads was 150 mg.
TABLE 3
______________________________________
Residual Concentrations and Decomposition Ratios of Dioxins
(treatment temperature 250.degree. C.)
Residual
concentration decomposition
Examples Compound (ng/g) ratio
______________________________________
8 aniline 210 84.2%
9 n-propylamine 350 73.8%
10 ethylenediamine 100 92.5%
11 aminomethylpropanol 300 77.5%
12 ammonia 810 39.3%
______________________________________
It is evident from Table 3 that the amine compounds used in Examples 8
through 12 also give a high decomposition ratio of dioxins.
Industrial Applicability
As described in detail in the above, according to the method of the present
invention for the decomposition of dioxins, dioxins are decomposed and
eliminated in a short time, and in a low temperature range in which
usually dioxins decomposition does not occur. This brings about a decrease
in the energy cost required for the treatment and improvement in the
effectiveness of the treatment, resulting in the considerable decrease in
the total cost of the treatment. Moreover, since the method of the present
invention does not require a reductive treatment atmosphere so that the
treatment can be performed in the open air or in the flue gas, the method
can be conducted with simple treatment equipment and easy operation.
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